Farmers utilize a wide variety of tillage implements to prepare soil for planting. For example, a strip tillage implement is capable of tilling soil in strips along the intended planting rows, moving residue to the areas in between rows, and preparing the seedbed of the strip in preparation for planting. As another example, a field cultivator is also capable of simultaneously tilling soil and leveling the tilled soil in preparation for planting. A tillage implement, whether of the strip tillage variety or of the traditional field cultivator variety, has a frame that carries a number of cultivator shanks which can carry various tools at their lower ends for tilling the soil such as shovels, knives, points, sweeps, coulters, spikes, and plows. Each performs a function intended to ultimately convert compacted soil into a level seedbed with a consistent depth for providing desirable conditions for planting crops. Grass or residual crop material disposed on top of the soil is also displaced from the seedbed or worked into the seedbed so that it does not interfere with a seeding implement subsequently passing through the seedbed. Other devices attached to the tillage implement may perform functions such as inserting fertilizer following passage of the cultivator shanks, closing the furrow created by the cultivator shanks, or breaking up the clods to create the uniform seedbed.
It is well known in the art to provide tool assemblies for tilling the soil that are attached to shanks by way of a single side mounting between the tool assembly and the shank using ordinary fastener hardware. This allows easy replacement of the tool assembly as needed due to wear and breakage. Often, the shank is offset at one end, so that the tool assembly remains on the centerline of the tool and shank assembly. One or more of the fasteners connecting the working part of the tool assembly, such as the shovel, knife, point, sweep, coulter, spike, or plow, to the remainder of the tool assembly sometimes acts as a shear member, so that upon contact between the working part of the tool and a resistant object, such as a rock, the fastener shears, thereby minimizing breakage of the working part of the tool.
Because of the single side mounting between the tool assembly and the shank, the fasteners connecting the tool assembly to the shank are in single shear. Furthermore, as the tool assembly flexes under the load of being drawn through the soil, it may flex somewhat from side to side, as well as flexing backwards. This results in cleavage forces at the point where the fastener connects the tool assembly to the shank. As a result, these fasteners commonly fail during use. Worse, in the process of failing or yielding the tool assembly tends to depart from proper forward alignment, so that the tool assembly, or the working part of the tool particularly, breaks or is damaged due to side loads.
If the tool assembly remains attached to the shank and to the tillage implement, it may then be permanently deformed so that it operates out of alignment with the direction of travel of the tillage implement. Such alignment of the shank and tool assembly with the direction of travel of the tillage implement is critical to proper operation of the tillage implement. Continued use of a shank and tool assembly in a deformed state is detrimental to the performance of the tillage implement, not only because that particular shank and tool assembly does not perform its function correctly, but also because the deformed shank and tool assembly generates uneven drag or even acts as a rudder, pulling the remainder of the tillage slightly sideways. This reduces the performance of the other shank and tool assemblies, and other devices attached to the tillage implement, and further requires greater tractive effort on the part of the tractor to move the tillage implement through the soil.
What is needed in the art, therefore, is a way to more closely control the conditions under which a tool assembly shears away from a shank upon contact between the working part of the tool and a resistant object such as a rock. Further, a way is needed to prevent secondary damage to the tool assembly or detrimental performance of the tillage implement due to ongoing misalignment of a bent tool assembly or due to side loads during the process of shear separation from the shank.